Suggested Approach

It is doubtful that creating a single Excel application to support all 180-plus Office languages will make economic sense, but the time spent making your application support a few of the more common languages will often be a wise investment. This will, of course, depend on your users, and whether support for a new language is preferable to new features.

The approach that I take is to write the application to support multiple languages, and to provide users with the ability to switch between the installed languages or conform to their choice of Office UI Language. I develop the application in English, and then have it translated into one or two other languages depending on my target users. I will only translate it into other languages if there is sufficient demand.